The present invention relates to a ferromagnetic structure of an ion source produced by permanent magnets and solenoids. It is applicable in ion sources of the electron cyclotron resonance type, where it confines the plasma of a gas or vapour in which the ions are produced by impacts of ionizing electrons.
U.S. Pat. No. 4,417,178, filed in the name of the Commissariat a l'Energie Atomique describes a heavy ion source of the ECR type (electron cyclotron resonance), called "Micromafios", in which the magnetic confinement configuration of the plasma is produced by the superimposing of a magnetic induction with an axial component produced by solenoids and an induction with a radial component produced by permanent magnets based on rare earths (such as e.g. samarium-cobalt).
The useful volume to be magnetized is approximately 1 liter. The electric power consumption of the solenoids is approximately 100 kW, i.e. relatively high for ensuring a maximum induction of 0.5 Tesla in this useful volume.
There is still an internal demagnetizing field superimposed on the external field of a straight permanent magnet, whose origin is the reclosing of the magnetic flux between the opposing poles. This situation makes it necessary to arrange sufficiently long magnetized bars to minimize the influence of the opposing pole in the useful volume.
FIG. 1 shows the configuration of the permanent magnets according to the prior art in the Micromafios source.
In the case of the magnetic structure of the source according to the aforementioned patent, the magnets 1 have a length L of 7 cm to obtain 90% of the magnetic induction in the useful volume 2. In theory, it would by necessary to have a bar of infinte length L to obtain 100% of this maximum induction. The volume of this configuration, as well as the quantity of magnetized material are high in this magnetic structure.